Promising that as a "citizen-politician" he would reverse the "cynicism and mistrust" of the American people towards their leaders, Bill Bradley returned to his home town on the banks of the Mississippi yesterday to launch a crucial phase of his increasingly serious challenge to Al Gore for the Democratic party presidential nomination.

Without mentioning President Clinton or Mr Gore, the former basketball star and senator promised supporters at his former high school in Crystal City that he would fight "to restore trust in public service and confidence in our collective will".

Mr Bradley stressed how he lacked "a famous name or great wealth" but was given "the encouragement and love and the opportunity that enabled me to forge a path on my own". His speech was full of memories of a riverside childhood "where the world of possibility and hope all began".

Those possibilities have looked even broader since a weekend poll showed him running neck and neck with the vice-president in the New Hampshire primary contest which in five months' time will launch a highly compressed primary season.

Mr Bradley underscored his down-home message by leading a posse of press and local activists on a tour of his boyhood sites, culminating in the supreme Bradley shrine, the basketball hoop which still stands in the back yard of his childhood home. At it, the gangly teenager honed the skills that made him a legend during his 10-year career with the New York Knicks in the 1960s.

Mr Bradley's launch offered few detailed policy ideas, in contrast to a series of recent campaign speeches by Mr Gore.

But his campaign, which once seemed little more than a worthy but quixotic sideshow to the apparently irresistible coronation of the vice-president, has gradually acquired a professionalism and momentum which genuinely threatening Mr Gore.

He is attracting interest from a media pack that sniffs the possibility of a real contest. That process was given a huge push at the start of this week, when a Boston Globe poll in New Hampshire showed Mr Bradley had 36% support in the Democratic primary race, only four percentage points behind Mr Gore, a gap that fell within the poll's margin of error. Furthermore, 39% of Democratic voters polled said it was time for a change in political leadership.

Mr Bradley's fundraising success, particularly among the party's rich Silicon Valley and Wall Street backers, is also worrying the Gore camp. In July, Mr Bradley impressed the party by reporting $11.7m raised in the first six months of the year, compared with Mr Gore's $17.5m. That has helped to keep the money rolling in.

Compared with Mr Gore, Mr Bradley has so far picked up relatively few formal endorsements, but he has the backing of the former Federal Reserve bank chairman, Paul Volcker, media mogul Michael Eisner and retiring New York senator Daniel Patrick Moynihan, as well as the more glamorous endorsements of actor Harrison Ford and basketball legend Michael Jordan.

Yesterday's campaign launch was an attempt to package an image which is one of Mr Bradley's most obvious advantages over Mr Gore. It cast him as the hard-working small-town boy, son of a bank manager and a Sunday school teacher, who worked his way up as a model student to become successively a Rhodes Scholar, an Olympic athlete and a sports legend, before 18 years as a cerebral, and fairly conservative, Democratic senator for New Jersey.

But, as Mr Gore counter-attacked this week on health care reform, the key question remains Mr Bradley's ability to surf the political mainstream. He needs to show he can mount a more credible challenge than the vice-president to the likely Republican nominee, the centrist Governor George W Bush of Texas.

Both Democrat contenders are naturally cautious and centrist, and Mr Bradley has been careful not to parade himself as the liberal alternative .

Instead, he has confined his major policy lines to proposing a radical shake-up in campaign finance laws - an issue on which the vice-president is especially vulnerable - and to promoting a tougher gun reform package than the one put forward by the administration.